[#127] Starter kit and sub theming docs

[jacine]

Fixes #127.

As mentioned in #127, the following issues need to be worked out before this is merged.

• [radix] [Task] Provide a means to rename other additional configuration files
• [radix] [Task] Drush subtheme generator expects the kit to be located in Radix

[jacine]

It's worth noting that you can't really test this ATM, as those 2 Radix issues (which @arshad has already started to work on) really are needed.

I have committed the kit here, verbatim, which would allow you to run the command, and get past the Drush subtheme generator expects the kit to be located in Radix: drush --include="web/themes/contrib/radix" radix:create "subtheme" --kit=https://github.com/jacine/radix-kit-apigee_custom/archive/master.zip

However, if you test, you will notice that not all of the configuration files are renamed properly, due to the other issue: Provide a means to rename other additional configuration files.

[shadcn]

The two Radix issues are now completed and in the latest dev release.

https://www.drupal.org/project/radix/issues/3081166
https://www.drupal.org/project/radix/issues/3081150

I tested this PR and everything is working. I'm going to go ahead and merge this. I'll create a follow up PR to update Radix to the latest stable release.

Thanks @jacine

[shadcn]

Tested and approved. Thanks @jacine

[jacine]

Thank you @arshad! I just tested the Radix issues and they're both good to go. 👏